The absorption spectrum of collagen is investigated in the far- infrared wavelength region. Initial measurements on films cast from solutions of (rat tail tendon) collagen in the region from 500-20cm to the -1 power (20-500 micron) reveal six well-resolved absorption bands obtained with an instrument resolution of 1-2cm to the -1 power. The spectrum contains bands which are sensitive to conformational changes and characteristic of the motions of large segments of the molecule. Band assignments are made and checked by studying the effect of temperature, sample orientation and water and n-alcohol content on the collagen spectra and by investigating the spectra of synthetic model compounds, such as poly(proline-glycine-proline), which possess structural and physical properties similar to those of collagen. The collagen-gelatin transition is investigated by observing changes in the far-infrared spectrum as the collagen samples are heated through the melting temperature. The results are compared with calculations on the melting of model triple-helical molecules found in the literature.